Made my room into a camera obscura today and then posted a picture of the project image online. A friend of mine commented on it with a link to a photographer who had done some camera obscura work but their images were right side up on the wall. I assumed this was done using photoshop but she said she read he uses a prism to correct the projected image? Is there any truth to this and if so, how does it work and what shape prism would be used? Any information would be great, thanks.